Cats are usually trained to use a litter box for elimination of both liquid and solid wastes. A cat litter box is normally made of plastic or like material so that a cat's urine will not leak through the box. Other cat litter boxes have been proposed, as in the construction described in U.S. Pat. No. 5,249,549 (Rockaitis), in which the litter box is made of a material that absorbs liquid but does not permit it to leach through to the exterior of the box. The litter used in boxes of this kind may be one of any number of particulate litter or other materials that absorb moisture from the waste of the cat. The material may also suppress odor from cat waste. Some forms of cat litter form clumps when wet. Usually, a cat will bury its solid waste in the litter material in the box.
Most cat owners take appropriate action to discard the litter from a cat litter box after an appreciable period of time, often several days. On the other hand, even before the litter has been thoroughly saturated with waste from the cat or cats that use it, a cat may be inclined to push some of the litter out of the box, particularly if the odor is strong. In any event, the person using a cat litter box may find the task of emptying the cat litter to be unpleasant. Thus, a number of devices have been proposed for cleaning cat litter boxes. Such devices are disclosed in U.S. Pat. No. 4,096,827 (Cotter), U.S. Pat. No. 4,117,804 (Moore et al.), U.S. Pat. No. 4,190,525 (Menzel), U.S. Pat. No. 4,325,325 (Larter), U.S. Pat. No. 4,325,822 (Miller), U.S. Pat. No. 5,048,465 (Carlisi), U.S. Pat. No. 5,226,388 (McDaniel), and U.S. Pat. No. 5,477,812 (Waters).
The self-cleaning cat litter box disclosed in the Carlisi patent utilizes a rake or comb that is normally maintained in a storage position at one end of the litter chamber. At predetermined intervals, the comb is moved through the litter, from the rake storage end of the chamber to the opposite end, which constitutes a discharge end for the chamber. At the discharge end of the chamber the rake moves up out of the litter and discharges any clumps collected by the comb into a disposal receptacle. Unfortunately, because cats are not consistent in their elimination habits, such periodic clearing may be too frequent, or not frequent enough.
The Waters patent describes a system for moving a comb or rake through the litter responsive to entry and exit of the cat from the litter box. In addition, Waters provides an improved disposal receptacle and alarms to report an insufficient litter supply and a full disposal receptacle. The entire disclosure of the Waters '812 patent is incorporated herein by reference.
Despite the advances made by these prior art patents, there remains several deficiencies in self-cleaning litter boxes. First, if the cat is present in the litter box while the rake or comb is moving, the cat may be startled to move suddenly and spill the contents of the litter box or, the cat could be caught by the mechanism. Second, devices that require the passage of time or the activity of a cat to initiate the rake drive mechanism do not allow for use of the rake at other times. Third, easy access is needed to aid cats in entering and exiting the litter box. The open boxes allow litter to be spilled out and do not provide cover for cats that may desire privacy.